Digital communication techniques are widely employed in many different types of communication systems. Generally, use of digital communication techniques permits the communication of data at significantly higher data throughput rates, with greater efficiency, than that permitted through the use of conventional, analog communication techniques. Information that is to be communicated is converted, or otherwise provided, in digital form. Typically, the data is formatted pursuant to a standardized, formatting scheme, known to both a sending station at which the data originates and a receiving station at which the data terminates. The sending and receiving stations are interconnected by way of a communication channel upon which the data is communicated. In a radio communication system, the communication channel is defined, at least in part, upon a radio link extending between the communication stations.
In an actual communication system, the communication channel is imperfect. That is to say, the data is sometimes distorted during its communication upon the communication channel. The informational content of data, once received at the receiving station, is distorted. If the distortion is severe, the informational content of the data cannot be recovered.
Various schemes have been developed that provide manners by which the distortion introduced upon the data is corrected or by which to compensate for the distortion. Coding of data, prior to its communication, to increase its redundancy is one such type of scheme. And, communication of known values, or sequences of values, is sometimes also used to determine whether data received at a receiving station has adequately been decoded.
An exemplary, digital cellular communication system, a GPRS/EDGE (general packet radio service/enhanced data for GSM evolution) cellular communication system, communicates coded data between sending and receiving stations pursuant to effectuation of an EDGE communication service. Data formatted into radio blocks are sent by the sending station to the receiving station. A radio block includes a header part and a payload part. And, the payload part of the radio block includes a 12-bit CRC (cyclic redundancy code), and, optionally, is FEC-protected. The header part of the radio block includes an 8-bit CRC and is also FEC (forward error correction)-protected more strongly than the payload part. The CRC of the payload part of the radio block is used to determine whether the payload part has been correctly decoded. However, it is sometimes possible for an erroneous determination to be made that the payload part has been decoded correctly even when the payload part has been decoded incorrectly. That is to say, an erroneous determination is made. With the CRC of a 12-bit length, a random data block is likely falsely to pass the CRC check once every 4,096 times. In a lengthy data transfer, tens of thousands of radio blocks might be received. In bad signal conditions, a few corrupt radio blocks will pass the CRC check and be accepted as valid, in error.
Once the data is accepted as valid, the data is passed to a higher logical layer to form part of a data block, a PDU (packet data unit). The higher-layer, data block is formed of, typically, dozens of lower layer radio blocks. If a bad, i.e., corrupted, radio block forms part of the higher-layer data block, the higher data-layer data block is also corrupted. When the corruption is detected, a complete retransmission of all of the radio blocks of the higher-layer data block might be caused to ensue, resulting in significant delay, and much unnecessary retransmission. Additionally, the higher-layer retries are sometimes based on timeouts. Corruption at the higher layers might further stall data flow until a timer expires and triggers a retransmission of the data block. Stalled data flow leads to poor data throughput rates.
An improved manner by which better to ensure that a corrupted radio block is not erroneously accepted as valid would therefore be advantageous.
It is in light of this background information related to communication of data using digital communication techniques that the significant improvements of the present invention have evolved.